Generation and modulation of electric waves



March 8, 1932.

R. A. HElSlNG GENERATION AND MODULATION OF ELECTRIC WAVES Filed Aug. 18 192 2 Sheets-Sheet l Arron/[r March 8, 1932. R. A'.- HEISING 1,348,126

GENERATION AND MODULATION 0F ELECTRIC WAVES Filed Aug. 18 192' 2 Sheets-Sheet 2 4-@2 A a-a3 10/10 C/RCIII T ATTORNEY 1 tal controlled oscillator,

this harmonic quency high frequency and Patented Mar. 8, 1932 UNITED STATES PATENT OFFICE NEW YORK,

NEW JERSEY, ASSIGNOR TO WESTERN ELEC- N. Y., A CORPORATION OF NEW GENERATION AND MODULATION or ELECTRIC WAVES Application filed August 18, 1927. Serial No. 213,761.

This invention relates to generation and control of electric waves.

An object of the invention is to produce modulated waves free from undesired frequency variations.

In one specific aspect the invention is a system in which signal waves are applied to an electric space discharge tube oscillator for modulating oscillations which it generates, and a control generator is coupled to the oscillator for stabilizing its frequency, the oscillator being tuned approximately to. a harmonic of the frequency at which the control generator operates.

The control generator may be a frequency stabilized oscillator, for example, a piezoelectric crystal controlled oscillator, operating at a given frequency and producing a harmonic wave of the given frequency and impressing the harmonic wave on the other oscillator, which is tuned approximately to frequency. The harmonic power from the control generator pulls the other oscillator into step, even though the pulling power may be very much smaller than the power in the second oscillator. Thus, a first oscillator, for example, the crysof relatively low frequency and power, can stabilize the freof a second oscillator, of relatively power, and the second oscillator can have the waves which it generates modulated in accordance with signal waves which may be supplied to the plate circuit, for example, of the second oscillator.

If desired, the hi h power or second oscillator may be tune to the same frequency as the low power or first oscillator, instead of to a harmonic frequency.

Systems of the types described above have important advantages over a system comprising an oscillatei" for controlling an amplifier-modulator. For example, they require less control power, and they utilize singing and hence avoid any necessity for preventing singing in high frequency amplifier circuits. Moreover, if the second or power oscillator is tuned to a harmonic of the frequency at which the first or crystal controlled oscillator operates,

plate circuit of the tube.

as mentioned above, the frequency of the second oscillator can be higher at which crystals can be operated satisfactorily.

If desired, the second oscillator, instead of having its output current modulated, may control a third oscillator, of higher power or frequency or both, to which signal waves may be supplied for modulating the oscillations generated in the third oscillator. The third oscillator may be tuned approximately to a harmonic of the frequency to which the sec-' ond oscillator is tuned,the second oscillator then producing this harmonic of its base frequency and impressing it on the third oscillator. Similarly, four or more oscillators may be employed, the signal waves being supplied to the last oscillator to-modulate its output current.

Instead of having the controlling harmonics produced in the oscillators themselves, non-oscillatory ,harmonic producers (that is, harmonic generators which do not produce self-sustained oscillations) may be inserted between the oscillators, to control the second oscillator from the first oscillator, the third oscillator from the second oscillator, etc.

Other objects and aspects of the invention will be apparent from the following description and claims.

In the drawings, Fig. 1 is a circuit diagram of a short wave radio transmitting system embodying a form of the invention; Fig. 1A indicates a modification which may he made in the system of Fig. 1; Fig. 2 is a circuit diagram of a system embodying an other form of the invention, for producing signal modulated waves and Fig. 3 is a circuit diagram of a system embodying still another form of the invention.

In Fig. 1 an oscillator O-1 comprises an electric space discharge tube 1. The fundamental frequency of the oscillator is determined largely by the capacity C and the inductance L connected in parallel in the The inductance coil L is coupled to a feedback coil 10 in the grid circuit of the tube.

A. harmonic of the oscillator frequency is than the maximum frequency ductance coil 22 in selected by the capacity C and the inductance L in parallel in the plate circuit, and is impressed on the grid circuit of an electric space discharge tube oscillator O2.

The oscillator O-2 comprises an electric discharge tube 2 having a capacity C and an inductance L in parallel in its plate circuit. The inductance coil L is coupled to the feedback coil 15 in the grid circuit of the tube 2. Oscillator O-2 tends to oscillate at a frequency set by L and G at approximately the desired harmonic of the first oscillator and as near to the harmonic selected by Lg and 0;. as convenience in the setting permits. The harmonic power from the first oscillator pulls the second one into ste A harmonic of the frequency of the second oscillator is selected by the capacity C. and the inductance L circuit, and is impressed on the grid circuit of an electric space discharge tube power oscillator O3.

The oscillator 0-3 which may contain any desired number of tubes is shown as comprising two space discharge tubes 3 in parallel, coupled to an antenna 20 through an inductance coil 21 in the antenna and an inparallel with a capacity 23 in the plate circuit of the tubes. The coil 21 is coupled to a feedback coil 24 in the grid circuit of the tubes. The frequency of the power oscillator is determined largely by the antenna circuit, and is very close to the resonant frequency L and C The harmonic power of the second oscillator pulls the third one into step with the harmonic frequency.

Plate-current is supplied to the oscillators from source 25, that for tube 1' assing through inductances L and L, that or tube 2 passing through L and L and that for tubes 3 passing through coil 22. p

The grid circuit of each oscillator includes acondenser C and a grid leak resistance R for supplying grid biasing potential. A condenser 30 in each oscillator by-passes high frequency current around the plate current source and prevents that source from polarizin the oscillator grid or grids.

The frequency of the primary oscillator O1 may be stabilized in any satisfactory manner.

The output current of the power oscillator O3 is modulated in any suitable way and undesired variations of its frequency, which might result from the modulating operations or from other causes, are prevented since the controllin harmonic frequencies from oscillators (%-1 and O2 synchronize oscillators O-2 and 0-3 with those frequencies respectively. Any two consecutive oscillators, and therefore all of them, may be tuned to the same frequency, as explained in the fifth paragraph of this specification.

in parallel in the platev In the system shown, modulation is accomlished by the constant current method. ignal currents, for example, speech currents from telephone transmitter 35, are amplified in amplifier A 36, which feeds electric space discharge amplifying tubes 37. The tubes 37 supply signal currents to the oscilaltor 0-3, for modulating the output current of the power oscillator, and are known as the modulator. The modulator is designated M38. Space current for tubes 37, as well as the space current for tubes 3, is supplied by source 25 through a choke coil 39 which has high impedance for the speech or other signal frequencies.

Fig. 1A shows a modification of the connections shown in Fig. 1 between oscillators O1 and O2. In Fi 1-A the capacity O is across the secondary, instead of the primary, winding of the coupling transformer including inductance L In Fi 2, a Colpitts oscillator O1, as disclose for example in U. S. patent to Colpitts 1,624,537, granted April 12, 1927, has its oscillation circuit, comprising inductance L in parallel with two series connected capacities O1, tuned approximately to the mechanical resonance frequency of a piezo-electric crystal 40 which stabilizes the oscillator frequency. The source 25 supplies space current for tube 1 through a choke coil 41 that has high impedance for waves generated by oscillator O1'. A condenser 42 prevents this source from polarizing the crystal.

A harmonic of the oscillator frequencyis selected by the capacity 0 and the inductance L in parallel in the plate circuit, and is impressed on the grid circuit of a Hartley oscillator O2, of the type disclosed for example in U. S. patent to Hartley 1,356,763, granted October 26, 1920.

Oscillator O2 tends to oscillate at a frequency set by its oscillation circuit L and G at approximately the resonance frequency of L and C The harmonic power of the first oscillator pulls the second one into step.

A harmonic of the frequency of the second oscillator is selected by the capacity O and the two inductances L1, and is impressed on the grid circuits of each of tubes 3 of a push-pull electric space discharge oscillator O3. The circuit constituted by capacity C in parallel with the two inductances L1 in series, is connected in series in the plate circuit of oscillator 0-2. One of the coils L; impresses the harmonic voltage from oscillator O2 on the grid of one of tubes 3, and the other of the coils L1 impresses the harmonic voltage on the grid of the other tube 3 in opposite phase or sign.

The oscillator O3 tends to oscillate at a frequency set by its oscillation circuit L and C, at approximately the resonance frequency the coil,

of C, with inductances L1. The harmonic power of the second oscillator pulls the third one into step. The source 25 supplies space current to the tube 2 through one half of coil L and coils L1.

The connection 45 to the inductance L is intended to represent any suitable load circuit for the oscillator -3, as for instance an antenna, or amplifier stages or a transmission line connected to an antenna.

The inductance L is a bifilar coil comprising two strands 47 and 48. Condensers 49 connect the strands together at each end of and condenser 30 connects the strands together at the middle of the coil. Each of these three condensers has low impedance for frequencies of the order of the oscillation frequency; and the two strands 47 and 48 act as a single inductance at such frequencies.

The filaments of the two tubes 3 are conductively connected to the middle of strand 48. The grid of one of the two tubes is conductively connected to the filaments through a grid leak resistance and a portion of strand 48 at one side of the middle of the strand.

The grid of the other tube 3 is conductively connected to the filaments through a grid leak resistance and a portion of strand 48 at the other side of the middle of the strand.

Source supplies space current for the tubes 3 through choke coil 39, the current for one tube passing through one half of strand 47 and the current for the other tube passing through the other half of strand 47.

The oscillations generated in power oscillator O-3' are modulated in any suitable way, and undesired variations in the oscilla- -'tor frequency, which might result from the modulating operations or from other causes, are prevented since the controlling harmonic frequencies from oscillators O1 and O-2 synchronize oscillators O-2 and O3 with those frequencies respectively.

In the system shown, modulation is accomplished by the constant current method. Signal currents, for example, speech currents from transmitter 35, are amplified in amplifier A36 which feeds the amplifying tubes 37 that supply signal currents to oscillator 0-3, for modulating the oscillations generated by the oscillator. As indicated above, the element of the circuit formed by the tubes 37 may be called the modulator and is designated M-38. The space current for tubes 37, as well as that for tubes 3, is supplied from source 25 through the choke coil 39, which has high impedance for signal frequencies. Condensers and 49 also have high impedance for the signal frequencies.

The circuits described above for producing signal modulated waves, although well adapted to serve as short wave radio transmitters, are free from high frequency amplifiers. The harmonics are produced in the oscillators 65 themselves and taken out through appropriate 'mary oscillator does not voltage-output current characteristic.

circuits and impressed upon the succeeding oscillators. The primary oscillator may be stabilized in any satisfactory manner or crystal controlled as indicated in Fig. 2. In the systems of Figs. 1, 1-A and 2, the prihave to be any of the arrangements shown, even through crystal controlled, but may be of any form in which there is an inductance in the circuit from which to get harmonics or in which an inductance or tuned circuit may be inserted to select the harmonics. Any two consecutive oscillators, and therefore all of them, may be tuned to the same frequency, as explained in fication.

In Fig. 3 a tuning fork oscillator 0-51, operating at a frequency of, for example, 1000 cycles a second, feeds an amplifier A-62 which in turn feeds a harmonic generator HG63.. Oscillator 0-51 comprises a tuning-fork 51 actuated by a magnet 52 which has its winding included in circuit with a coil 53, a suitable source of current 54, and an interrupting or resistance changing device 55 mechanically actuated by a tine of the tuning fork. The fork is thus arranged to automatically control the energization of the magnet 52 so that the action of the fork will be continuous to supply a periodically variable current to the coil 53. The coil 53 is coupled to a coil 56 in the input circuit of amplifier A-62. The amplifier A62 may be, for example, a space discharge amplifier operating on the straight portion of its irglput he harmonic producer HG-63 may be of any suitable type, as for example, the non-oscillatory electric space discharge harmonic generator disclosed in Venues Patent 1,485,650, March 4, 1924. In the output circuit of the harmonic producer is a circuit 65 tuned to a frequency, say, 10,000 cycles per second, which is a harmonic of the frequency of oscillator A Hartley oscillator O comprising an electric space discharge tube 70 has in its oscillation circuit a condenser 71 in parallel with inductance coils 72 and 73 in series.

The tuned circuit 65 is coupled to coil 73, and the oscillation circuit of tube 70 is tuned approximately to the same frequency as circuit 65. Therefore, theoscillator is held in step with the 10,000 cycle current in circuit 65, although the oscillator output is much greater than the power of the controlling harmonic.

Space current for tube 70 is supplied by source 25 through a choke coil 75 that has high impedance for waves generated by oscillator'O-70. Condensers 76 and 77 prevent source 25 from being short circuited and prevent this source from polarizing the grid of tube 70. -A leak resistance 79 connects the grid and the filament of tube 7 0.

the fifth paragraph of the speci- A harmonic generator HG85 com rising the pulling power is very much smaller than an electric space discharge tube 85 as its rid and filament connected across resistance 9 by a series condenser 86 and a shunt resistance 87. A source 88 supplies a large nega-- tive potential to the grid of tube 85 to cause the tube to generate pronounced harmonics more efiiciently. Space current for tube 85 is supplied by source 25 through the output coil 90 of the tube. A condenser 30 by-passes alternating current around the source 25. The harmonic producer does not generate self-sustained oscillations.

A Hartley oscillator O91 comprising an electric space discharge tube 91 has in its oscillation circuit a condenser 92 in parallel with inductance coils 93 and 94 in series.

The coil 90 is coupled to coil 94, and the oscillation circuit of tube 91 is tuned approximately to a harmonic of the frequenc of oscillator O which is generated by armonic producer HG-85. Therefore the oscillator is held in step with that harmonic, although the oscillator output is much greater than the power of the controllng harmonic.

Space current for the tube 91 is supplied by source 25 through choke coil 39. The steady grid potential for this tube is determined by resistance 97.

A load circuit 95 of any suitable type is coupled to thecoil 93 by a coil 96.

In the system shown, modulation is accomplished by the constantcurrent method. Signal currents, for example, speech currents from telephone transmitter 35 are amplified in amplifier A36, which feeds electric space discharge amplifying tubes 37. The tubes 37 supply signal currents to the power oscillator O9l, for modulating the oscillations generated by the oscillator, and may be called the modulator. The modulator is designated M38. Space current for the tubes 37 as well as the space current for tube 91, is supplied from source 25 through the choke coil 39, which has high impedance for the currents of speech or other signal frequencies.

The power required to pull an oscillator into step depends upon the part of the circuit into which it is introduced and upon how much difference there is between the pulling frequency and the frequency at which the oscillator tends to work. A system works well in which the pulling power'is put into the oscillation circuit of the controlled oscillator directly, as for example, at coils 90 and 94 in Fig. 3; but the pulling power is more effective if it is put into the grid circuits of the controlled oscillators, as for example, in Figs. 1 and 2. On some occasions it is possible for a control current to pull an oscillator into step even where the frequency of the controlled oscillator is as much as 10% different from that of the control current and the power in the controlled oscillator. In arrangements as indicated in any of the figures of the drawings, the diflerent oscillators or stages do not have to be of the same power capacity but, as is indicated above, may actually mcrease in ower from the first towards the last and still secure frequency control.

What is claimed is:

In combination, an electric space discharge tube, means associated with said tube for causing it to generate self-sustained oscillations of approximately a given frequency, means supplying signal waves to said tube for modulating the waves generated by said tube, and means supplying to said tube waves of a frequency different from said given frequency, said frequencies being related as harmonic to fundamental.

2. In combination, means for generating a wave of a given fundamental frequency and a wave of a frequency which is higher than and harmonically related to said fundamental frequency,-a generator having means for causing its fundamental frequency to be substantially equal to said harmonic frequency, means so associating said first means and said generator of said second fundamental frequency that said harmonic frequency wave from said first means maintains said generator of said second fundamental frequency in synchronism with said first means, and means supplying signal waves to said generator of said second fundamental frequenc for modulating the wave generated thereby.

3. In combination, an oscillator operating at a relatively low frequency, a second oscillator associated therewith, tuned approximately to a harmonic of said first oscillator, means included in said first oscillam5 tor itself for producing said harmonic of said relatively low frequency for impression on said second oscillator, whereby said first oscillator controls the frequency of said second oscillator, and means supplying modulating waves to said second oscillator.

In combination, an electric space discharge device, means for supplying modulating waves to said device, means for causing said device to generate self-sustained oscilla- 115 tions of fixed frequency, and an oscillation generator coupled to said device, included in said last mentioned means, the power capacity of said device being large relative to that of said oscillation generator.

5. In a short wave radio transmitter, an oscillator of relatively low power capacity operating at a relatively low frequency, a second oscillator of relatively high power capacity tuned approximately to a harmonic 125 of said first frequency, means for supplying signal waves to said second oscillator for modulating the waves produced thereby, means included in said first oscillator itself for producing said harmonic, and means cou- 130 first means, coupled to said first means pling said oscillators for impressing said harmonic from said first oscillator on said second oscillator, whereby said first oscillator stabilizes the frequency of said second oscillator without the interposition of non-oscillatory high frequency amplifiers, and thus prevents frequency variations which might occur due to the modulating operations.

6. In combination, means for generating self sustained oscillations, a generator of self-sustained oscillations, having greater inherent frequency stability than said first means, coupled to said first means for stabilizing the frequency of said first means, and means coupled to said first means for supplying modulating waves thereto.

7. In combination, means for generating self-sustained oscillationsof frequency different from but harmonically related to a given frequency, a generator of self-sustained oscillations of said given frequency, having greater inherent frequency stability than sgid or stabilizing the frequency of said first means, and means coupled to said first means for supplying modulating waves thereto.

8. In combination, an oscillator operating at a given frequency, a second oscillator tuned approximately to a harmonic of said first frequency, means for supplying signal wavesto said'second oscillator for modulating the waves produced thereby, and means coupling said oscillators, having substantially the same transmission efliciency for energy transfer in opposite directions;

9. In combination, an oscillator having a space current circuit, a second oscillator of relatively low power and relatively high inherent frequency stability associated with said first oscillator for stabilizing the frequency of said first oscillator, and means for supplying signal waves to said space current circuit for modulating the waves generated by said first oscillator.

10. A signaling system comprising a relatively high power oscillator, an oscillator for delivering relativel low power at a frequency having less variation than the frequency variation that said first oscillator would undergo in the absence of said second oscillator, means coupling said oscillators for stabilizing the frequency of said first oscillator, and means supplying signal waves to said first oscillator for modulating the oscillations generated by said oscillator, the frequency to which one of said oscillators is tuned being an integral multiple of a frequency to which the other is tuned.

11. A signaling system comprising a relatively high power oscillator, an oscillatorfor delivering relatively low power at a fre- I a frequency equal to a harmonic of the fundamental frequency, means responsive'to the single wave constituted by said wave of fundamental frequency for converting the fundamental frequency wave into a wave ofa frequency which is a harmonic of the fundamental frequency equal to the harmonic generated by said second generator, means for so inter-relating said converting means and said second generator that the frequency of said second generator is maintained in synchronism with the harmonic produced by said converting means, and means supplying signal waves to said second generator for modulating the waves produced thereby.

13. In combination, an oscillation generator operating at a relatively low frequency, a second oscillation generator tuned approximately to'a second frequency which is a harmonic of said first frequency, an oscillator adjusted to oscillate approximately at a third frequency which is a harmonic of said second frequency, means for causing said first oscil-. lation generator to control the frequency of said second oscillation generator, means for causing said second oscillation generator to control the frequency of said oscillator, and means for supplying signal waves to said oscillator for modulating the waves generated by said oscillator.

In witness whereof, I hereunto subscribe my name this 16th day of August. A. D. 1927.

RAYMOND A. HEISING.

quency having less variation than the fresaid first oscillator quency variation that said second would undergo in the absence of oscillator, means coupling said oscillators for 

